Many polymerizable monomeric materials, and particularly vinyl chloride, are being polymerized today on a large scale commercially either in suspension media or in aqueous dispersion or emulsion, i.e., latex form, employing various colloidal suspension agents, emulsifiers or soaps, and/or synthetic detergent-type dispersing agents. In these methods of polymerization, and particularly in suspension polymerization, agitation (usually vigorous) is depended upon to suspend and/or disperse the monomer particles or droplets throughout the reaction media and to maintain such suspension or dispersion during the polymerization reaction and to assist in heat transfer to the reactor cooling surfaces. However, in most instances, polymer particles produced in accordance with these processes are not uniform in size and shape. In subsequent processing of these polymers, such as, for example, polyvinyl chloride (PVC), it is desirable to have uniform size and shape in the polymer particles.
Various polymerization processes and modifications of existing processes have been heretofore proposed to obtain uniform particle size. For example, one very successful method that has been proposed is that described in U.S. Pat. No. 3,620,988. In said method a monomeric material, such as vinyl chloride, of low solubility in water containing a monomer-soluble free radical type catalyst, is suspended as discrete droplets of a desired size in an aqueous medium thickened with a water-insoluble polymeric gellation agent which imparts plastic flow properties to such medium. The polymerization reaction is then carried out using a batch or continuous process under substantially quiescent conditions, that is, in the absence of turbulence or the absence of shearing forces sufficient to deform the suspended droplets of monomer and/or to damage the polymer bead at any stage of conversion. However, when polymerizing vinyl chloride by such a process, the uniform beads of PVC that are formed are normally clear and glassy in nature and do not have the desired porosity.
There are many cases where porous polymer particles or beads are desirable, such as where the polymer, such as PVC, is to be employed in making plastisols and in extrusion operations. Porous beads would also be desirable to the case of PVC where, because of Government regulations, it is necessary to remove substantially all of the unreacted vinyl chloride therefrom. Porous polymer beads or particles would greatly facilitate such removal. High bulk density is another desirable polymer property because it results in faster extrusion rates, easier handling and shipping advantages.
Thus a process which will produce vinyl resin particles which are spherical, and porous throughout and which have high bulk density is most desirous.